The present invention relates to a water-swellable crosslinked rubber conposition of which the swelling ratio with water is markedly insusceptible to compression of the material in a dry condition. More particularly, the invention relates to a water-swellable crosslinked rubbery composition comprising a blend of a chloroprene rubber and a highly water-absorptive resin as the essential components, of which the swelling ratio with water is little affected by the compression of the composition in a dry condition.
Water-swellable rubber compositions, as a class of newly developed products in recent years, are widely used as a sealing material in various portions of structured bodies where watertight sealing is required such as the sealing material for metal-, e.g. steel-made structured bodies, prefabricated culvert boxes, sealed segments, joints formed in the assembly of precast concrete bodies, construction joints and the like as well as a sealing material for repairing of structured bodies. In particular, it is taught in Japanese Patent Kokai No. 57-108143 that a very useful watertight sealing material is obtained with a composition prepared by dispersing a highly water-absorptive resin in a 1,3-diene-based synthetic rubber containing 5 to 50% of the crystalline or glassy region or, preferably, a chloroprene rubber containing 15 to 35% of the crystalline region, which rapidly absorbs water to give a high swelling pressure.
The watertight sealing material of this type, however, has a serious problem that, when the material undergoes a compressive deformation of 30% or larger in a dry condition, for example, in the course of construction of the structured body, the capacity of the material for the absorption of water is remarkably reduced so that the desired watertight sealing effect cannot be fully exhibited thereby to greatly limit the applicability of such a material.
Accordingly, it has been eagerly desired to develop a novel and improved watertight sealing material free from the above described problem in the prior art sealing materials or, in particular, a water-swellable rubbery composition which is insusceptible to compression in a dry condition capable of fully exhibiting the swelling capacity with water when released from the compression.